Reduction of arcing between the parts of a cathode ray tube



March 25, 1969 G, V. ANGELUCQ ET AL. 3,434,770

REDUCTION OF ARCING BETWEEN THE PARTS OF CATHODE RAY TUBE 4 Filed May19, 1967 FIGI HIGH VOLTAGE TRANSFORMER TIMER NO2 FIGZ RlcHARD J. KURTZRICHARD s. o'FALLoN BY QMQMMW ATTORNEYS I 4 .T 6 S l. e e C 4./.T S C VT9 .l Dn U No m O L CC T E N G E N e IM VA g N C 7 I V n z/rdm E WWS eo G@A OW R m A m G e r d 2 A r u mw C mm GF A 2 7 2 O 4 7 IL I, I 5 Ian/ w1MI nld, HI kn g .m 11:. IIIM f I u. w u \\w \m 4 O wav 3 3 l UnitedStates Patent O U.S. Cl. 316--1 9 Claims ABSTRACT OF THE DISCLOSURE Highvoltage aging of a cathode ray tube to neutralize arcing is accomplishedby placing a grounded metal band about the neck of the tube. The bandestablishes a ground plane about the neck in which electrical elds aredeveloped which simulate the iields developed during normal tubeoperation in a tele-vision receiver. A high aging potential is appliedbetween the final anode and the grids of the electron gun assembly,which are grounded, in stages from between 15,000 volts to 40,000 volts.During each stage the voltage is periodically boosted from 5,000 to10,000 volts over the stage voltage, for a predetermined time, to fosterarcing between the tube parts.

Cross-reference to related application Patent No. 3,321,263, issued May23, 1967, and assigned to the assignee of this application, describes aprocess for reducing arcing in a cathode ray tube.

Background of the invention Although the pieces of an electron gunassembly can be cleaned chemically, there still remains trace impuritieson the guns which are capable of undesired emission of electrons,Satisfactory processes have been developed for the reduction of arcingbetween the parts of the cathode ray tube in a color television receiverin which the electron gun structure includes a final anode operating ata potential on the order of 25,000 volts, and focus, screen and controlgrids operating at a potential from between 5,000 volts for the focusgrid to 130 volts for the control grid. Because of the potentialdifierence between the nal anode and the dilierent grids, this undesiredemission of electrons can foster arcing between the different gun parts,which is annoying to the viewer and harmful to the gun assembly.Generally, the practice in the past has been to hit the anode of thetube with a high potential with the grids grounded to arc out the tubeto burn otf the trace impurities from the gun. This arcing out isfollowed by high voltage aging at a potential of around 40,000 volts fortime in excess of 1 hour. The time required for the high voltage agingnecessarily adds to the production time required to make a tube.

Electron gun assemblies have been developed for cathode ray tubes usedin color television receivers, which are based upon a Zero focusprinciple. That is, the focus grid is coupled to a reference potentialand is positioned intermediate first and second accelerating electrodeswhich are electrically connected to one another by a shield which ispositioned about the focus electrode. A potential on the order of 25,000volts is coupled to the two accelerating electrodes. This brings thehigh voltage much further down into the neck of the tube as cornpared tothe conventional tri-beam electron gun assembly thereby increasing thearcing problem between the tube parts.

Summary It is an object of this invention to provide the method andassociated apparatus necessary for carrying out a high voltage agingprocess which reduces the production time required to make a cathode raytube.

It is another object of this invention to provide the method andnecessary apparatus for carrying out high voltage aging in a colortelevision tube that reduces the` tendency for arcing between the partsof the electron gun assembly when a high potential exists deep in thetube neck.

In practicing one embodiment of this invention, a tribeam electron gunassembly is mounted in the neck of a cathode ray tube used in a colortelevision receiver. Each gun includes a focus electrode connected to areference potential and positioned intermediate rst and secondaccelerating electrodes, which are connected to each other by a shieldpositioned about the focus electrode. The accelerating electrodes areconnected to a potential in eX- cess of 25,000 volts while the focuselectrode is operated at ground or at a relatively low referencepotential. The screen and control grids, which are also operated at arelatively low potential, are coupled along with the focus grid to stemconnectors supported in the tube stem. The gun electrodes are subject tocontamination by trace impurities which are capable of undesiredemission of electrons. The high voltage aging process of this inventionutilizes arcing to burn off these impurities, and high voltage aging toneutralize the impurities to reduce the possibility of arcing during thetube life. During the process, the tube stem connectors are grounded,grounding the focus, control and screen grids. A metal strap ispositioned about the tube neck and grounded. This metal strapestablishes a ground about the tube neck which simulates the groundplane formed about the neck of the cathode ray tube during normaloperation in a color television receiver, by such devices as theconvergence and deflection yokes. A high voltage on the order of 15,000volts is applied to the accelerating grids for a predetermined time.This voltage is increased briefly to 25,000 volts every few seconds tofoster arcing of the tube. After the predetermined time, the voltage isincreased to 25,000 volts and is periodically boosted to 30,000 volts.The aging potential is thus increased in stages until the base voltageis 40,000 volts, which is periodically boosted to 45,000 volts, At theend of the process, the trace impurities are burned od or areneutralized so that under normal tube operating voltages there will belittle chance of arcing between the parts of the electron gun assembly.

In the drawings:

FIG. 1 is a schematic showing of the apparatus used in the process ofthis invention;

FIG. 2 is a cross-section view of the neck portion of a cathode ray tubein accordance with this invention; and

FIG. 3 is a block diagram illustrating the steps of the process inaccordance with this invention.

Detailed description Referring to the figures of the drawing, FIG. 1shows a color cathode ray tube 10 which has a glass necked envelope 12,containing an electron gun assembly (FIG. 2) for producing threeelectron beams. The inside of the funnel portion 14 has an Aquadag(trademark of Achesorl Colloids Company `for their brand of colloidalgraphite in water) coating 16 extending a short distance along theinside surface of the neck envelope 12. The coating is electricallyconnected to a portion of the electron gun assembly. A face panel 18 isconnected to the funnel portion 14 and includes a shadow mask structure20 and a viewing screen 22 consisting of phosphor dots which'emitcolored light when impinged by an electron beam. The

viewing screen 22 is composed of triads of phosphor dots, with theapertures of the shadow mask structure restricting the beams toassociated ones of the dots and triads for reproducing a colored image.

FIG. 2 illustrates in detail the electron gun assembly within the neckportion 12 of the tube 10. The electron gun assembly includes threeelectron guns one of which is shown in detail at 25. In this view, onlya small portion 26 and 27 can be seen of the other two electron guns ofthe assembly. In the electron gun assembly 25, an electron beam isgenerated by a cathode (not shown), which is processed and acceleratedby the control electrode 30, a screen electrode 34 and rst and secondaccelerating electrodes 36 and 33. Positioned intermediate theaccelerating electrodes is the focus electrode 4t). A slightly curvedshield 42 provides electrical connection between the acceleratingelectrodes 36 and 38 and reduces exposure of these electrodes and thefocus electrode to the glass neck of the television tube. A convergenceassembly 45 is connected to the accelerating electrode 38 and completesthe electron gun assembly. The assembly 45 has a number of contacts 47connected thereto which electrically connect the assembly 45 to theinner Aquadag coating 16. The convergence assembly 45 converges threebeams from the electron gun into a single beam which is deected by thedeflection yoke (not shown) mounted to the shadow mask assembly in theknown manner.

In order to provide convenient points for connecting the cathode raytube to circuitry in a television receiver, the cathode, controlelectrode 30, screen electrode 34 and focus electrode 4t) are attachedto stem connectors 48, which are mounted exteriorly of the neck envelope12 in the stem piece 50. In addition, the Aquadag coating 16 is attachedto a terminal 52 (FIG. 1) mounted exteriorly of the funnel portion 14for connection to the receivers high voltage signal. The order ofmagnitude of the voltages which may exist at the connectors 48 and theterminal 52 are as follows. A direct current potential on the order ofkilovolts is applied to terminal 52 to establish the Aquadag coating 16,the convergence assembly 45, and the first and second acceleratingelectrodes 36 and 38 for each gun assembly at this 25 kv. potential. Thefocus electrode is connected through connector 4S to ground referencepotential, or to a potential which is relatively much lower than thepotential on the first and second accelerating electrodes, for instance,1 kv. The screen electrode 34 may be at 45() volts, the controlelectrode 32 at -20 volts and the cathode electrode at 20() volts.

By connecting the focus electrode 40 at or near ground potential,shielding the gaps between the first and second accelerating electrodes36 and 38 and the focus electrode 40 greatly reduces the possibility ofelectric elds within the tube neck causing convergence drift of theelectron beam that passes through the focus electrode 40 so that littleor no focusing of the electron beam during reception of a transmittedsignal will be necessary. This type of electron gun assembly is commonlyreferred to as operating on the zero focus principle.

Electrically connecting the first and second accelerating electrodes 36and 38, however, brings the high voltage potential of approximately 25kv. down much further into the neck 12 of the tube than is found inelectron gun assemblies for use in color television receivers where onlythe final anode is maintained at such a high potential. Furthermore,because the faceplate panel 18 is preferably rectangular in congurationwhen viewed from the front, and the tube has a relatively widedeflection angle of the beam (for example 90 or more), the overalllength of the tube may be made as short as possible, and the receiver inwhich the tube is used may be compact. However, reducing the dimensionsof the tube requires placing the electron guns in the assembly muchcloser together, for instance, in a typical tube the neck portion 12 maybe on the order of 11/2 inches in diameter. Due to the high potentialdifferences between the first and second acceleratng electrodes 36 and3S and the stem connectors 48 a current will flow through the glassenvelope to develop a charge thereon. Other factors contributing to thepresence of neck charge are cold emission from the electrodes to theneck, imperfections on the surface of the glass, and residue remainingthereon after the glass has been cleaned. Thus there may be arcingbetween the neck 12 of the tube, which can be at a potential as high as25,00() kv. or more and one or more of the electrodes 30 and 34. Theremay also be arcing between the various electrodes themselves becausethey are at widely different potentials and in closely spaced relationwithin the tube neck.

Patent No. 3,321,263, issued May 23, 1967, and assigned to the assigneeof this application describes a high voltage arc-out and aging processwhich substantially reduces the possibility of arcing among the gunparts. However, introducing a high potential deeper in the tube neck, asoccurs when using a zero focus-type electron gun assembly, has addedcomplications which this invention is especially suitable for curing.

Considering a time after the guns have been chemically cleaned and thetube is assembled with the gun in a tube ncck, which has been acidrinsed, the evacuated and sealed tube undergoes a getter hashing step 60(FIG. 3). This is a known process involving the activation of a gasabsorbing material within the bulb of the tube to reduce the residualquantity of gas remaining after vacuum pumping of the tube.

Following getter flashing, the turbe is ready for step 62, the highvoltage aging process of this invention. A braided copper strap iswrapped around the tube neck. The tube is supported in a vertical mannersuch that the neck portion 12 extends into a container 67 which containsa plurality of fibers of a good conducting material 69, for instance,steel wool. With the tube in this position, the stem connectors 48extend into the steel wool and make electrical connection therewith. Thebraided strap 65 has a portion which extends down the side of the tubeand into the steel wool. Another portion of the strap 72 extends fromthe container 67 and is connected to a suitable ground referencepotential. With the strap 65 connected to ground, the focus electrode4G, screen electrode 34 and control electrode 32 are all maintained at aground potential through the stern connectors 48.

With the tube in this position, a pair of Variacs (trademark ot GeneralRadio Company) 7d and 72 are connected to a high voltage transformer 74.The output o the high voltage transformer' 74 is connected throughresistor 75 and coupled 'by lter capacitor 77 to the anode 52 of thetube It). A pair of timing devices 78 and 80 operate respectivesolenoids 82 and 84 for applying the preselected outputs of Variacs '70and 72 to the high voltage transformer.

In this aging process, a high voltage is applied to the anode 52 inincreasing stages commencing with 15 kv. and ending with 40 kv. Duringeach stage, the aging voltage is periodically boosted from 5 to 10 kv.above the stage voltage to foster arcing between the tube parts. Forinstance, in a typical first stage, a 15 kv. potential is applied to theanode 52 for a period of 3 minutes. During this three minute period, the15 kv. potential is alternately applied every 5 seconds, with a 10 kv.booster potential which raises the potential to 25 kv., for 2 seconds tofoster arcing. The aging potential will cause the trace impurities onthe electron guns to emit electrons as cold emitters, or due to electricfield emission. As an example of a trace impurity or contaminant,consider silicon or oxide silicon on the surface of one of theelectrodes which would emit electrons under the aging potential- Thiselectron emission will cause ionization of any residual gasses in thetube which have not been absorbed in the getter flashing step 60, and ablue glow may be noted in the region of the neck 12 of the tube. Withthe residual gasses thus ionized, these ions tend to strike or bombardthe emissive contaminants on the surface of the gun electrodes to poisonthem, or

render them less effective as electron emitters. Accordingly, througheach stage of this process, the blue glow gradually diminishes sincecold emission is reduced and, therefore, the ionization of the residualgasses is reduced. At the same time, the arcing which is periodicallyinduced in the tube by the addition of the Ibooster potential at eachstage tends to burn or melt any of the foreign particles, sharp points,or imperfections on the electron gun assembly to eliminate the gunassembly of the trace impurities which can cause arcing. The resistor 75is on the order of 60K ohms to limit the current that can pass throughthe gun parts to insure that they are not damaged during the process.Furthermore, the arcing is only carried out Afor a very short time,i.e., two seconds and then stopped by reducing the potential back to thestage base potential. Therefore, the arcing is prevented from becomingregenerative and possibly burning up the gun parts.

The following table illustrates one schedule that was satisfactorilyfollowed in accordance with the principles of this invention. It issignificant that the combined high voltage aging and arc-out processonly consumed a total of 35 minutes of time, and the tube subsequentlysatisfactorily passed a test where a test potential was supplied insteps from 30 kv. to 40 kv. and no arcing was indicated.

In this illustration, Variac 70 could be used for applying the basepotential in stages, and Variac 72 could be adjusted to provide thebooster potential for each stage. Timers 1 and 2 may be any commerciallyavailable timing mechanism which would be operated to alternatelyenergize solenoids 82 and 84 to apply the potential in 5 or 2 secondsteps as required.

Due to the fact that the high voltage operating potential of the tube isbrought down much further in the neck of the tube than with theconventional tri-beam electron gun, it is necessary, in order to get theproper arcing action along the tube neck during the high voltage boostphase of each stage of the process, to place the metal band 65 about thetube neck 12 as shown in FIG. 2. This metal band establishes a groundplane about the tube neck and exterior to it which develops electricfields about the neck when the agingpotential is applied between the gunparts. With this band in place, vicious arcing between the tube partscan be observed, which does an excellent job in burning olf the tracecontaminants. An important characteristic of the braided strap is thatit forms a ground plane about the neck of the tube and electrical iieldsthereabout which actually simulate the ground plane and iieldsestablished about the neck of the tube by such devices as theconvergence and deflection yokes under normal operating conditions in acolor television receiver. It was found that without this metal strapencircling the tube, the process was not nearly as effectual inproducing the desired result. The strap 65 may be located anywhere alongthe neck of the tube but it was found that best results were obtainedwith the strap positioned about the neck of the tube in the vicinity ofthe convergence assembly 45. Furthermore, the invention is notnecessarily limited to the use of a metal strap, as other devices couldbe used satisfactorily, For instance, a foil of a good conductingmaterial could be completely wrapped about the neck of the tube andextended the length thereof. With this type of application satisfactoryresults were also obtained.

Referring once again to FIG. 3, after the high voltage aging process thecathode is activated in step 64, by providing a current to the lament ofthe cathode, considerably in excess to normal operating current, forhigh heating of the cathode as is known in the art. Activating thecathode takes approximately 30 minutes. In step 90 the cathode is agedat a potential reduced from that necessary to activate the cathode.Cathode aging requires from l to 2 hours. After aging of the cathode, anouter Aquadag coating is added to the tube at step 92, and is followedby step 94, which is a nal test to insure that the tube meets themanufacturers specifications.

What has been described, therefore, is a method and the necessaryapparatus for conducting a high voltage arc-out and aging process whichreduces the production time for a cathode ray tube, and which greatlyreduces the probabilities of arcing between the electron gun parts in acolor television tube with the high voltage operating potential broughtfar down into the neck of the tube.

We claim:

1. A process for reducing the tendency of arcing among the parts of acathode ray tube having an electron gun structure positioned in the tubeneck which includes a plurality of grids subject to contamination bytrace impurities capable of undesired emission of electrons, and a finalanode to be established at an operating potential substantially greaterthan at least one of the grids, the process including the steps of,establishing a ground plane on the outer surface of the tube neck,applying a high voltage age potential in increasing stages between theanode and the grid, and increasing the high voltage age potential for apredetermined interval during each stage to induce arcing within thetube.

2. The process of claim 1 wherein the high voltage age potential isincreased in stages from ybetween 10,000 volts to 50,000 volts.

3. The process of claim 1 wherein the: increase in the high voltage agepotential for a predetermined interval during each step to induce arcingis from. about 5,000 to 10,000 volts above the stage potential.

4. A process for reducing the tendency for arcing among the parts of acathode ray tube having an electron gun structure which comprises aplurality of grids including a focus grid coupled to a referencepotential and positioned intermediate lirst and second acceleratingelectrodes which are electrically connected to each other by a shieldpositioned about the focus grid and are operated at a potentialsubstantially greater than the focus grid, and wherein the grids aresubject tot contamination by trace impurities capable of undesiredemission of electrons, the process including the steps of, getterflashing the tube, establishing a ground plane about the outer surfaceof the tube neck, applying a high voltage aging potential in increasingstages between the rst and second accelerating electrodes and the grids`of the electron gun assembly, and periodically boosting the highvoltage age potential for a predetermined interval during each stage tofoster arcing between the tube parts thereby ionizing the residualgasses within the tube to render the trace impurities ineffectual tocause arcing with the normal tube operating potential on theaccelerating electrodes.

5. The process of claim 4 wherein the normal operating voltage on theiirst and second accelerating electrodes is on the order of 25,000volts, and the high voltage age potential is increased in steps frombetween 15,000 to 40,000 volts.

6. The process of claim 5 wherein the booster voltage to induce arcingduring each step is from 5,000 to 10,000 volts above the step potential.

7. Apparatus for reducing the tendency in a television receiver forarcing among the parts of a cathode ray tube having an electron gunstructure positioned in the tube neck which includes a plurality ofgrids subject to contamination by trace impurities capable of undesiredemission of electrons, and a final anode to be established at anoperating potential greater than at least one of the grids, theapparatus including in combination, a high voltage source, timing meanscoupled to the voltage source for controlling the same to apply apredetermined voltage to the nal anode of the electron gun assembly fora predetermined time, means for connecting the plurality of grids of theelectron gun assembly to a reference potential, and electricalconducting means encircling the tube neck and being connected to areference potential, said conducting means developing electrical fieldsabout the tube neck to simulate the environment surrounding the sameduring normal operation thereof in a television receiver.

8. The apparatus of claim 7 wherein the conducting means includes agrounded metal strap encircling the tube neck.

9. The apparatus of claim 7 in which the electron tube further includesa stem member supporting a plurality of connector pins, each of which isconnected to a respective grid of the electron gun, and the apparatusfurther includes a container holding a plurality of metal bers, saidcontainer being positioned so that the connector pins extend into saidcontainer and contact said metal fibers thereby grounding the grids ofthe electron gun.

References Cited UNITED STATES PATENTS 3,323,854 6/1967 Palac 316-1RICHARD H. EANES, JR., Primary Examiner.

U.S. Cl. X.R.

